The exhaust gas emitted to an exhaust treatment system from an internal combustion engine is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter. Catalyst compositions, typically disposed on catalyst supports or substrates, are provided in various exhaust system devices to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
An exhaust treatment technology in use for high levels of particulate matter reduction, particularly in diesel engines, is the Particulate Filter (“PF”) device. There are several known filter structures used in PF devices that have displayed effectiveness in removing the particulate matter from the exhaust gas such as ceramic honeycomb wall flow filters, wound or packed fiber filters, open cell foams, sintered metal fibers, etc. Ceramic wall flow filters have experienced significant acceptance in automotive applications.
The filter in a PF device is a physical structure for removing particulates from exhaust gas and, as a result, the accumulation of filtered particulates will have the effect of increasing the exhaust system backpressure experienced by the engine. To address backpressure increases caused by the accumulation of exhaust gas particulates, the PF device is periodically cleaned, or regenerated. The regeneration operation burns off the carbon and particulate matter collected in the filter substrate and regenerates the PF device.
Regeneration of a PF device in vehicle applications is typically automatic and is controlled by an engine or other controller based on signals generated by engine and exhaust system sensors such as temperature sensors and back pressure sensors. The regeneration event involves increasing the temperature of the PF device to levels that are often above 600C in order to burn the accumulated particulates.
One method of generating the temperatures required in the exhaust system for regeneration of the PF device is to deliver unburned HC (often in the form of raw fuel) to an oxidation catalyst (“OC”) device disposed upstream of the PF device. The HC may be delivered by injecting fuel (either as a liquid or pre-vaporized) directly into the exhaust gas using an HC injector/vaporizer. The HC is oxidized in the OC device resulting in an exothermic reaction that raises the temperature of the exhaust gas. The heated exhaust gas travels downstream to the PF device to thereby burn (oxidize) the particulate accumulation.
A challenge for designers, especially those involved in space limited automotive applications, is that injecting fluids such as HC into the exhaust gas upstream of an OC device, or any other device for that matter, must allow for sufficient residence time, turbulence and distance in the exhaust flow for the injected fluid to become sufficiently mixed with and vaporized in the exhaust gas prior to entering the device. Without proper preparation, the injected fluid will not properly oxidize in the OC device and some unburned HC may pass through the device. The result is wasted fuel passing through the exhaust treatment system and uneven temperatures within the devices. Turbulators (i.e. static mixers) or other mixing devices may be installed in an exhaust conduit that fluidly connects the various exhaust treatment devices to aide in mixing the injected fluid. Such mixing devices, while effective, may add undesirable backpressure to the exhaust treatment system, reducing engine performance.
A technology that has been developed to reduce the levels of NOx emissions in lean-burn engines (ex. diesel engines) that burn fuel in excess oxygen includes a Selective Catalytic Reduction (“SCR”) device. An SCR catalyst composition disposed in the SCR device preferably contains a zeolite and one or more base metal components such as iron (“Fe”), cobalt (“Co”), copper (“Cu”) or vanadium (“V”) which can operate efficiently to reduce NOx constituents in the exhaust gas in the presence of a reductant such as ammonia (“NH3”). The SCR catalyst may be applied as a wash coat to either a conventional flow-through substrate or on the substrate of a particulate filter. The reductant is typically delivered as a liquid upstream of the SCR device, in a manner similar to the HC discussed above, and travels downstream to the SCR device to interact with the SCR catalyst composition; reducing the levels of NOx in the exhaust gas passing through the SCR device. Like the HC discussed above, without proper mixing and evaporation, the injected reductant, urea or ammonia for instance, will not properly function in the SCR device and some of the fluid may pass through the device resulting in wasted reductant as well as reduced NOx conversion efficiency.
Typical exhaust treatment systems may include several exhaust treatment devices as described above. In many instances, whether historical or not, the devices may comprise individual components that are serially disposed along an exhaust conduit that extends from the exhaust manifold outlet of the internal combustion engine to the tailpipe outlet of the exhaust treatment system. A challenge with this configuration is that it is necessary to choose a reasonable length between components, as well as sufficient mixing devices disposed within the exhaust conduit, to achieve adequate mixing of injected fluids (ex. HC and Urea (ammonia) reductant). As vehicle architectures become smaller, the desired length for an exhaust treatment system may not necessarily be available.
Accordingly it is desirable to provide an apparatus that will achieve uniform mixing and distribution of a fluid injected into the exhaust gas in an exhaust treatment system in a compact distance.